Inclusion Body Myopathy (IBM) associated with Paget's disease of the bone (PDB) and Frontotemporal Dementia, (IBMPFD, OMIM 167320), was first reported in 2000 by Kimonis et al. [1], and mapped to the human chromosomal region 9p13.3-12[2],[3]. In 2004, the disease was attributed to mutations in the gene encoding Valosin-Containing Protein (VCP) [4]. Classic symptoms of VCP disease include weakness and atrophy of the pelvic and shoulder girdle muscles in 90% of individuals [1-3]. Affected individuals exhibit scapular winging and die from progressive muscle weakness and cardiac and respiratory failure typically in their 40s to 50s [1, 5]. Histologically, patients show the presence of rimmed vacuoles and TAR DNA-binding protein 43 (TDP-43)-positive ubiquitinated inclusion bodies in the muscles [1, 4, 5, 6]. The variable phenotype is often diagnosed as limb girdle muscular dystrophy (LGMD), amyotrophic lateral sclerosis (ALS), facioscapular muscular dystrophy (FSHD), or scapuloperoneal muscular dystrophy (SPMD) [5, 7, 8]. To date, 31 VCP mutations have been reported in families from several parts of the world including Germany [9, 10], France [11], Austria [12], Italy [13, 14], the UK [15], Australia [16], Brazil [17], Korea [18], Japan [19] and the US [20, 21]. VCP mutations have been noted in 2-3% of isolated familial amyotrophic lateral sclerosis (fALS) cases [22], and 10-15% of individuals with hereditary inclusion body myopathy have an ALS-like phenotype characterized as a progressive neurodegenerative disease involving both upper motor neurons (UMNs) and lower motor neurons (LMNs) [5]. In order to understand the cellular and molecular pathophysiological mechanism(s) underlying VCP-associated neurodegenerative diseases, Applicants generated a unique CRE-ER™-VCPR155H/+ TAMOXIFEN™-inducible mouse model. This technology allows determination of the effects of targeted excision of exons 4 and 5, including the R155H mutation, in VCP disease. Applicants administered pregnant dams with 0.12 mg/g body weight TAMOXIFEN™ or corn oil by oral gavage and monitored their survival and muscle strength of the pups until 18 months of age. The TAMOXIFEN™-treated CRE-ER™-VCPR155H/+ mice demonstrated improved muscle strength and quadriceps muscles fiber architecture, reduced expression of autophagy markers, reduced brain neuropathology, decreased apoptosis, and partially rescued Paget's disease of bone. Parallel studies using splice switching therapeutics, which exclude or promote retention of specific exons as necessary, have been used successfully in muscle degenerative diseases such as Duchenne muscular dystrophy (DMD-exon skipping) and spinal muscular atrophy (SMA-exon retention).
Recently, VCP has also shown to play a critical role in maintaining mitochondrial quality and dynamics in the PINK1/Parkin pathway, whereby pathogenic mutations in VCP lead to an impairment in proteasome-dependent degradation [23]. Other studies have demonstrated the autophagic mechanism of VCP regulation and function, an important process in mediating protein degradation for terminally differentiated cells. Autophagy is responsible for degrading defective organelles and the bulk of cytoplasm during starvation. Recent studies have shown that sequestosome 1 (p62/SQSTM1) interacts with the autophagic effector protein Light Chain 3 (LC3B-I/II) to mediate the autophagic uptake of aggregated proteins. VCP is important for the retro-translocation of misfolded endoplasmic reticulum (ER) proteins, and failure in this activity results in defective endoplasmic reticulum associated protein degradation (ERAD) and ER stress responses [24]. Interestingly, the SQSTM1 gene, which encodes p62/SQSTM1, is involved in autophagy, and apoptosis, and is responsible for approximately 10% of sporadic PDB and 50% of familial PDB and mutations in p62/SQSTM1 have now been associated with ALS. Autophagic degradation is also involved in Alzheimer's and Huntington's diseases, among other neurodegenerative diseases [25-29].
Generation of TAMOXIFEN™-inducible Cre models has become the gold standard for determining gene function in mice by allowing the phenotypic analyses for selected tissues during embryonic development, thus, providing a powerful platform to analyze the functions of genes and proteins physiologically in vivo. Recent studies based on novel gene, cell and drug therapies in patients have shown promising exon skipping strategies to treat muscular dystrophies such as Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD) [30, 31], and in another autosomal dominant disorder fibrodysplasia ossificans progressive (FOP) by reducing the excessive activin receptor-like kinase 2 (ACVR1/ALK2) in FOP patients [32].
There is disclosed herein a transgenic CRE-ER™-VCPR155H/+ mouse model, with the targeted excision of the VCP R155H mutation that demonstrates amelioration of the typical phenotypic features observed in VCP-associated diseased patients.